The present invention relates to a valve control system for an internal combustion engine, and more particularly, to such a system of the type which can be used to deactivate the engine poppet valves of a number of different cylinders. The present invention also relates to an improved deactivating-type hydraulic lash adjuster (HLA) for use in such a valve control system.
Variable valve control systems of the valve deactivation type for engine poppet valves are already generally well known in the art. Although such valve deactivation type valve control systems can be applied to either the intake poppet valve, or the exhaust poppet valve, or both, it is most common to utilize such a valve deactivation system to select between the activated and de-activated conditions of only the intake poppet valves, and the invention will be described in connection with such a system.
Valve control systems of the type including “valve deactivation” capability are now well known to those skilled in the art. One embodiment of a valve deactivation control system is illustrated and described in U.S. Pat. No. 6,321,704, assigned to the assignee of the present invention and incorporated herein by reference. In the valve deactivation system of the cited patent, there is an HLA which may be operated in either: (a) a latched condition, in which case the rotation of the camshaft will result in normal valve lift, or (b) an unlatched condition, introducing lost motion into the valve gear train, whereby rotation of the camshaft will result in very little lift, or more commonly, no lift at all, of the particular intake poppet valve.
In order to gain a better understanding of the significance of the present invention, it is important to understand that most of the systems which have been referred to by the phrase “valve deactivation” have, in fact, been “cylinder deactivation” systems. In a cylinder deactivation system, only a portion of the cylinders are deactivated. For example, on a V-8 engine, it would be typical to provide valve deactivation capability for both the intake poppet valves, and the exhaust poppet valves, for two (the “deactivation” cylinders) of the four cylinders on each bank of cylinders. Therefore, as the engine speed and load increase and reach predetermined values, all of the valves for those two deactivation cylinders of each bank would be deactivated, such that the engine would then effectively operate on four cylinders (i.e., as a “V-4” engine) at highway speeds and low throttle loads. As is well known to those skilled in the art, in the example discussed above, the four cylinders still operating when the engine is cruising at highway speeds and low throttle loads are not provided with any means of deactivation (i.e., of either the intake or the exhaust poppet valves).
Cylinder deactivation, in which the effective displacement of the engine is reduced at cruising (highway) speeds, is utilized primarily to be able to improve fuel economy of the engine, at least over a portion of the engine operating cycle (i.e., at highway speeds and low engine loads). By way of contrast, a true “valve deactivation” system would be utilized on an engine of the type having two intake poppet valves for each cylinder. Although not an essential feature of the invention, it is typical on such engines (i.e., and particularly on direct fuel injection, Diesel type engines) that one intake poppet valve controls “swirl” while the other intake poppet valve controls “tumble”. Those skilled in the art of internal combustion engines will understand the meaning of the terms “swirl” and “tumble” and therefore, no further explanation of those terms will be included herein. Although the present invention is not so limited, the valve deactivation system of the present invention was developed for use on an engine of the type described above, such that the valve deactivation system is utilized to deactivate the tumble intake valve for each and every cylinder, and the invention will be described in connection therewith.
In a typical, tumble intake valve deactivation system of the type to which the present invention relates, the tumble intake valve is deactivated while the engine is operating in a range anywhere from idle speed up to some predetermined engine speed (e.g., 2000–2500 rpm), and load (anywhere from 0–75%), as is well known to those skilled in the engine art. The deactivation of the tumble intake poppet valves is done to increase the turbulence within the combustion chamber, in order to achieve faster, and more complete, combustion, resulting in reduced emissions.
Typically, the various roller followers and HLA's which have been utilized in cylinder deactivation systems have been of the type which are spring biased into latching engagement, and the latch member is moved toward the unlatched condition (valve deactivated) by hydraulic pressure. Although this known arrangement for achieving deactivation of an engine poppet valve has proven to be generally satisfactory in its limited commercial usage, there are certain inherent disadvantages in such a system. With the unlatched condition being accomplished by pressurized engine oil, it thus becomes necessary to provide within the cylinder head two separate hydraulic circuits, one to achieve normal cylinder head lubrication (and lubrication of the valve gear train components), and the other hydraulic circuit to achieve unlatching of the latch members of the HLA's of the valve deactivation system. As will be understood by those skilled in the art, the circuit which performs the cylinder head lubrication may be simply a constant, pressurized source, and at a relatively low pressure. On the other hand, the hydraulic circuit utilized to achieve the unlatching of the latch members must be controllable on command, thus typically requiring at least one electrically controlled solenoid valve per cylinder head.
In addition, by utilizing a hydraulic circuit within the cylinder head to control the unlatching operation, the control logic for the deactivation system must now be able to take into account the changes which occur in certain system variables, such as oil pressure, oil temperature, and oil viscosity. In addition, any degradation in the condition of the oil (i.e., cleanliness, chemical composition, etc.) will have a negative impact on the operation of the unlatching system, as will the amount of air in the oil.